Evidence tier
Moderate
Research weight
Citations
22 verified / 22
Classification
Performance
❝
What the evidence says. Several controlled trials; effects real but modest or context-dependent.
What is L-Citrulline?
L-Citrulline is a performance supplement used for increased nitric oxide. NutriDex grades the human evidence as Moderate. L-citrulline raises plasma arginine and nitric oxide more effectively than arginine itself, improving blood flow. Trials show modest gains in high-intensity endurance, more reps to fatigue, and reduced post-exercise soreness. It also produces small reductions in blood pressure. Effects are real but modest and somewhat inconsistent between studies.
Purported Benefits
✓Increased nitric oxide
✓Reduced muscle soreness
✓Endurance & pump
✓Blood pressure
Evidence by outcome
The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| Blood pressure / vascular functionMeta-analyses (15 RCTs) lower systolic BP ~4 mmHg and improve flow-mediated dilation in older adults; consistent, modest. | Moderate | ↑ benefit · small | 4 |
| Resistance-exercise reps/enduranceVårvik meta found ~6% more reps and a 2025 RCT raised muscular endurance, but a strength meta showed no effect; mixed. | Mixed | ↔ mixed · small | 3 |
| Aerobic/endurance performanceSeveral meta-analyses and a 2025 RCT show no effect on time-to-exhaustion or VO2; endurance ergogenic claim not supported. | Moderate | — no effect · negligible | 4 |
| Muscle soreness (DOMS)Meta-analysis (13 trials) reduced soreness at 24-48 h and lowered RPE, but not at 72 h; mostly 8 g citrulline malate. | Moderate | ↑ benefit · small | 2 |
| Lower-limb strength/function in older adults (with exercise)Meta-analysis (7 RCTs, 303 overweight >55) improved 6-min walk and leg strength, but only combined with exercise. | Preliminary | ↑ benefit · small | 1 |
| Erectile function (mild ED)Single small crossover RCT (24 men) normalized erection hardness in 50% vs 8% placebo; needs larger confirmation. | Preliminary | ↑ benefit · moderate | 1 |
Dosing & Compounds
Typical Dose
6–8 g citrulline malate (or ~3–4 g pure L-citrulline) ~60 min pre-exercise.
Active Compounds
Safety & Cautions
Very safe, well tolerated. Caution if on nitrates or BP medication. Educational only — always check with your doctor or pharmacist before combining L-Citrulline with any medicine.
Key Studies ★ 22 studies
Meta-analysis
Harnden 2023 (meta-analysis)
✓ PubMed
Meta-analysis of 9 RCTs (158 young healthy adults) found no significant effect of acute citrulline on endurance performance (time-to-exhaustion or time-to-completion).
Meta-analysis
Luo 2025 (systematic review/meta-analysis)
✓ Full text
Meta-analysis of 15 RCTs (415 middle-aged/older adults) found L-citrulline/watermelon intake significantly lowered systolic BP by 4.02 mmHg and diastolic BP by 2.54 mmHg.
Meta-analysis
Body composition meta-analysis 2025
✓ PubMed
Dose-response meta-analysis of 21 RCTs found citrulline/watermelon had no overall effect on body composition, with exploratory reductions in fat mass only at doses >6 g/day or in those over 40.
Meta-analysis
Arterial stiffness/endothelial meta-analysis 2025
✓ Full text
Meta-analysis of 8 RCTs (176 middle-aged/older adults) found L-citrulline significantly improved flow-mediated dilation (WMD 1.81%) but did not significantly improve overall pulse wave velocity.
meta-analysis
Buckinx / overweight older adults meta-analysis 2023 (PMID 37711701)
✓ PubMed
Meta-analysis of 7 RCTs (303 overweight adults over 55) found citrulline combined with exercise significantly improved 6-minute walk test (SMD -0.28) and lower-limb strength (SMD -0.38) versus exercise plus placebo.
meta-analysis
Tan 2023 inflammation/oxidative-stress meta-analysis (PMID 37111214)
✓ PubMed
Meta-analysis of 7 RCTs found L-citrulline/L-arginine did not significantly affect post-exercise oxidative stress (p=0.24), antioxidants (p=0.68), IL-6 (p=0.05), or IL-10 (p=0.34), with low to very-low GRADE certainty.
Meta-analysis
Food Sci Nutr 2026
✓ Full text
Meta-analysis of 6 RCTs (n=162) found L-citrulline reduced cold-induced systolic BP by 9.28 mmHg (95% CI −10.66 to −7.90, p<0.001) and diastolic BP by 5.33 mmHg (95% CI −9.38 to −1.27, p=0.01).
Systematic review
Bahari 2026
✓ Full text
Systematic review of RCTs evaluating citrulline (direct or via watermelon) in postmenopausal women reported benefits on vascular outcomes (blood pressure, arterial stiffness, endothelial function) with limited and inconsistent effects on muscular and metabolic parameters.
Meta-analysis
JISSN 2023
✓ Full text
Meta-analysis of 9 studies (n=158, young healthy adults) found citrulline did not improve endurance: time-to-exhaustion pooled SMD 0.03 (95% CI −0.27 to 0.33) and time-to-completion SMD −0.07, indicating no significant ergogenic effect on endurance.
Meta-analysis
Luo et al. 2025 (Clin Nutr ESPEN)
✓ PubMed
Meta-analysis of 15 RCTs (415 middle-aged/elderly participants): L-citrulline supplementation/watermelon intake significantly lowered systolic BP by -4.02 mmHg (95% CI -6.54 to -1.50; P=0.002) and diastolic BP by -2.54 mmHg (95% CI -4.27 to -0.81; P=0.004); combined L-citrulline + L-arginine was superior, reducing SBP by -10.44 mmHg and DBP by -4.86 mmHg.
Meta-analysis
Makama et al. 2025 (BJOG)
✓ PubMed
Systematic review/meta-analysis (20 RCTs, 2028 women) of L-arginine and its precursor L-citrulline in pregnancy: L-arginine reduced pre-eclampsia risk (RR 0.52, 95% CI 0.35-0.78) and severe pre-eclampsia (RR 0.23, 95% CI 0.09-0.55); the single L-citrulline trial (36 women) showed no effect on pre-eclampsia or BP, so direct L-citrulline evidence remains insufficient.
Meta-analysis
Vårvik 2021 (meta-analysis)
✓ PubMed
Meta-analysis of 8 RCTs (137 participants) found acute 6-8 g citrulline malate produced a small ergogenic effect, increasing strength-training repetitions by about 6.4% versus placebo.
Meta-analysis
Aguiar & Casonatto 2022 (meta-analysis)
✓ PubMed
Meta-analysis of 4 RCTs in resistance-trained adults found citrulline malate did not significantly improve muscle strength (SMD 0.13, 95% CI -0.21 to 0.46).
systematic-review/meta-analysis
Rhim 2020 soreness/RPE meta-analysis (PMID 33308806)
✓ PubMed
Systematic review and meta-analysis of 13 trials (206 participants, mostly 8 g citrulline malate) found citrulline significantly reduced muscle soreness at 24 h and 48 h and lowered RPE, but did not reduce soreness at 72 h or blood lactate.
Meta-analysis
Viribay et al. 2022 (Nutrients)
✓ PubMed
Systematic review/meta-analysis of 10 RCTs: citrulline supplementation showed NO significant benefit on aerobic exercise performance (SMD 0.15, 95% CI -0.02 to 0.32), perceived exertion, VO2 kinetics, or lactate; only a non-significant positive tendency for chronic dosing.
Meta-analysis
d'Unienville et al. 2021 (J Int Soc Sports Nutr)
✓ PubMed
Large meta-analysis (118 studies; 3 L-citrulline food-source studies) found NO effect of L-citrulline-rich foods on endurance performance (SMD -0.03, P=0.24), in contrast to trivial-but-significant benefits from nitrate- and polyphenol-rich foods (SMD ~0.15-0.17).
RCT
Frontiers Sports Act Living 2025 (DOI 10.3389/fspor.2025.1627743)
✓ Full text
Double-blind randomized crossover trial in 20 healthy adults found 10 days of L-citrulline (mean 7.4 g/day) did not improve time to exhaustion (20.5 vs 19.8 min, p=0.43) or cardiorespiratory responses, with only a non-significant trend in females.
RCT
JISSN 2025
✓ Full text
6-week double-blind RCT in 33 resistance-trained men: both L-citrulline and L-citrulline DL-malate significantly improved upper-body muscular endurance vs placebo and raised post-exercise nitric oxide, with no difference between the two citrulline forms and no strength benefit.
RCT
Cormio et al. 2011 (Urology)
✓ PubMed
Single-blind placebo-controlled crossover trial (24 men, mild ED): L-citrulline 1.5 g/day normalized erection hardness (score 3 to 4) in 50% of men vs 8.3% on placebo (P<0.01) and increased monthly intercourse frequency (1.4 to 2.3, P<0.01), with no adverse events.
Review
Trexler 2019 / Gonzalez 2017 reviews
✓ PubMed
Improved strength-endurance and reduced fatigue.
Study
Figueroa 2017
✓ PubMed
Lowered blood pressure and improved vascular function.
Study
Pérez-Guisado 2010
✓ PubMed
Citrulline malate increased reps and reduced soreness.